Analysis of the βNiAl Coating Conditions using an In-Situ Chemical Vapour Deposition Technique

A. D. CHANDIO, M. A. KALHORO, S. T. IQBAL, K. A. KALHORO

Abstract


Ni based super alloys have been used for blades and vanes of the aeroengine hardware. The main purpose of these alloys is to provide the high temperature strength under aggressive environments. However, the alloying elements used donor yield the desired resistance against oxidation to the components. In order to provide optimum oxidation resistance and enhance engine working efficiency, a system of the coating is applied which is usually called thermal barrier coating or TBC system typically comprising of two films or layers i.e. ceramic one which is topcoat (TC) and an underlying metallic layer as a bond coat (BC). One of the crucial parts of the TBC system is the nickel aluminides (βNiAl) that are used as BC material. This research involves the preparation of the nickel aluminide coatings onto CMSX-4 superalloy using pack or in-situ chemical vapour deposition (CVD) method. Coating quality produced is dependent on the processing parameters or conditions consequently influencing the TBC lifetimes. Therefore, this research investigates the influence of (in-situ CVD) processing parameters i.e. Al contents, time, temperature, and activator contents on the βNiAl coatings. The coating characterisation was carried out by utilising field emission scanning electron microscope (FESEM) equipped with EDS and powder X-ray diffraction (XRD). The results demonstrated that all of these parameters affect the coating thickness and micro structural evolutions significantly except activator which has mild effect. In particular, coating time was observed to be more pronounced i.e. coating thickness was found to be increased proportionally as the time. The discussion is presented on the deposition mechanisms and micro structural features of the coatings.

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